Japanese Published Patent Application No. 082 029 67 describes use of a fire detector having a video camera as an imaging device. The video camera is placed in a tunnel, and the recording signals of the video camera are converted into a digital signal via an analog-digital converter. The digital signals are stored, and a processor implements a brightness histogram. A determination as to whether a fire exists or not is made by comparing the pixel number to a particular brightness value.
U.S. Pat. No. 5,289,275 describes a comparison of edge images with a reference image. In this context, individual images are compared to the reference image. Furthermore, it is described that radiant energy is derived from one image to recognize a fire. The fire is detected by an image in this case. In doing so, the extent of the flames is analyzed in order to subsequently estimate the radiant energy in conjunction with a temperature measurement, which leads to a decision as to whether a fire exists or not. In the process, transitions in the radiant energy are also taken into account from sample to sample.